FIG. 1 shows the basic structure of a HDD. When the HDD accesses data on a magnetic-recording disk 101, an arm 102 pivots so as to move a magnetic-recording head 103, which is provided at a front end of the arm 102, in proximity with a target servo track 104. The arm 102 has a structure such that the arm 102 pivots on a pivot axis 105; and, the arm 102 includes a drive mechanism, which is an actuator 106, at a rear end of the arm 102. When the actuator 106 moves the arm 102 to place the magnetic-recording head 103 at the target servo track 104, the position of the magnetic-recording head 103 is detected. For this purpose, a servo sector on the servo track is used.
The servo sector, shown in FIG. 2, includes an address code 201 and a burst signal 202. The servo sectors are radially written on the magnetic-recording disk 101. A servo track number and a serve sector number are recorded in the address code 201 in the form of Gray code. Thus, the position of the magnetic-recording head 103 over the magnetic-recording disk 101 is known. The burst signal 202 is used to control the position of the magnetic-recording head 103 to be accurately at the center of the servo track 104. The method called the 4th burst, shown in FIG. 2, has a structure in which four patterns form a set; and, the boundary of two bursts is defined as a servo track 104.
Among the methods for writing this servo track 104, a method referred to herein by the term of art, “called a self-servo writing,” is known in the art, by which servo tracks are written using a magnetic-recording head in a HDD after the HDD is assembled. Engineers and scientists engaged in HDD manufacturing and development are interested in the design of HDDs that employ self-servo writing to provide written servo tracks on the magnetic-recording disk to meet the rising demands of the marketplace for increased data-storage capacity, performance, and reliability.